1. Field of the Invention
The present invention relates in general to an air conditioner for automobiles, and in particular to an improved air conditioner for automobiles of the type having an auxiliary air mixture door for improving the mixing of hot and cold air streams, which is arranged such that the air blowing-out rate can be mode constant.
2. Description of the Prior Art
It is known from Japanese Provisional Utility Model Publication Nos. 191,513/1985 and 70,415/1988, for example, to provide an auxiliary air mixture door within a mixture chamber in the heater unit of an air conditioner for automobiles as a means for improving the mixing of hot and cold air streams in the air conditioner.
The air conditioner for automobiles disclosed in the latter publication comprises an intake unit 101, a cooling unit 102 and a heater unit 103, as shown in FIG. 5.
The intake unit 101 is formed with an interior-air intake 104 for introducing thereinto air from the room or interior of an automobile and an exterior-air intake 105 for introducing thereinto air from outside the room, with an intake door 107 being rotatably mounted for selectively opening and closing these intakes 104 and 105.
A fan 108 provided in the intake unit 101 serves to introduce air into the intake unit 101 and to drive the introduced air in the intake unit 101. The rate of air so introduced or driven is adjusted by controlling the speed of rotation of a fan motor 109.
The cooling unit 102 has an evaporator 110 provided therein, which is connected to a cooling cycle (not shown) for cooling the introduced air.
The heater unit 103 is provided with a heater core 111, to which a hot water pipe is connected for circulation of engine-cooling water. A bypass passage 112 is provided adjacent to the heater core 111 for conducting the air around the heater core 111. Upstream of the heater core 111, there is provided an air mixture door 113 which can be rotated to adjust the ratio of the amount of air passing the heater core 111 to the amount of air passing through the bypass passage 112.
Downstream of the heater core 111, there is formed a mixture chamber 115 where an auxiliary mixture door 150 is rotatably provided. For the purpose of minimizing the size of the heater unit 103 by making the auxiliary door 150 as small as possible, a fixed guide 120 which will not interfere with the flow of air through the bypass passage 112 is provided downstream of an air stagnation zone 119 located behind the heater core 111. When the mixture door 150 is rotated to a position C, the auxiliary mixture door 150 and the fixed guide 120 will cooperate to deflect the cold air flow through the bypass passage 112 toward the hot air flow which has passed the heater core 111, whereby the mixing of the cold and hot air streams can be facilitated.
Where an auxiliary mixture door is provided in the mixture chamber so as to deflect the hot or cold air flow thereby to improve the mixing function, however, there is a problem in that the auxiliary mixture door is still inevitably a resistance to the intake air flow which prevents a sufficient amount of air from being supplied through the air conditioner.
In addition, different rotated positions of the auxiliary mixture door may provide different air flow rates which may cause the driver or passengers to feel unpleasant or disordered.